Warm up weights for baseball bats are generally known. Such weights may be mounted on the shaft of the bat to provide extra weight in addition to the weight of the bat itself. The extra weight assists in warming up the batter during practice swings, such as might be taken during an “on deck” period in which the batter is waiting to take his or her turn at bat.
A common bat weight is known as a “donut” because of its donut-like shape. In geometric terms, this shape may be referred to as a “ring torus,” or simply “torus.” The ring torus has a hole through which the bat is inserted. Typically, the bat would be inserted handle-end-first. This is because the handle end of the bat is smaller than the striking end of the bat. Thus, when the handle-end of the bat is inserted in to the torus hole, the torus may be slid down the shaft of the bat until the diameter of the bat becomes larger than the diameter of the torus hole. At this point the torus stops. Another way of viewing the use of the donut is to slide the donut onto the handle-end of the bat, usually with the bat in a vertical orientation with the handle end above the striking end. Thus, the donut drops down the bat until it reaches the point where the bat diameter exceeds the donut-hole diameter and the donut stops. Often, a player will tap the bat on the ground to ensure that the donut stays in this position.
Commonly, baseball bat donuts are made of a weighted ring, coated in a rubber material that will hold the donut shape, but will give a little to tighten up the engagement of the donut with the bat surface. The donuts may come in different sizes and/or weights such that a player may put different or multiple donuts on a bat to achieve a preferred swing training, or warm up, weight.